One reason for the increased success of multi-user computing systems arises from the fact that their designs include substantial provisions for coping with power failures. Such systems have facilities that afford the user the luxury of experiencing a loss of primary power, and enable the system to resume processing as if no loss of supply voltage had been experienced. In general, such systems require battery back-up or some other power supply replacement that is activated in the event of a failure of the A/C main supply.
With the increasing complexity of multi-user computing systems,and a resulting geometric increase in the amount of available solid state memory in such systems, power fail protection requires substantially increased amounts of standby power. More specifically, the backup power supply must enable the data in the volatile memory bank to be stored prior to a total loss of supply voltage. The volatile memory must then be returned to the same state after power is restored. At typical speeds, using a disk to store data dumped from the volatile memory, substantial time may be required to accomplish such storage actions. For instance, if a multi-user system includes a 1-gigabyte quantity of data, such transfer would consume over 3 minutes of disk operating time. Future systems are expected to grow upwards of 4-gigabytes and thus, it would theoretically take over 10 minutes to save the data and another 10 minutes to reload.
Recent advances in the disk drives have led to the introduction of extremely small disk drives that are both inexpensive and high capacity. For instance, one such disk drive employs 1.3 inch disks, is smaller than a normal cigarette package, stores 40 megabytes and is available at a cost of less than $400. Such disk drives enable the storage of substantial amounts of data in a small package at very low cost.
Accordingly, it is an object of this invention to provide a data processing system with a volatile memory module whose contents are protected in the event of a power failure.
It is another object of this invention to provide a data processing system with power protected random access memory wherein nonvolatile memory modules are provided for the sole purpose of memory protection.
It is yet another object of this invention to provide a memory protection system that enables a computer, after a power-off and a subsequent power-on, to immediately reconstitute a memory state that existed at the power-off stage.